In the case of wind turbines, the output power of the wind turbine must be changed in the event of a change of frequency in the grid. In this case, it may be a requirement to reduce the power if the frequency increases. It is also known to operate the wind turbine in a throttled manner in order to be able to increase the power in the event of a drop in frequency. In the case of extreme frequency events in the grid, the power must be reduced to zero or the turbine must be isolated from the grid.
Methods such as this are known, for example, from DE 100 22 974 A1, from EP 1 790 850 or from WO 2010/000648 A2.
Said regulation is required since changes in the grid frequency are generally based on disturbances in the equilibrium of supply and demand in the grid. However, there are a multiplicity of grid events which have no influence on said equilibrium but are perceived as significant grid frequency disturbances within the grid measurement. By way of example, phase shifts in the case of switching processes in the grid may change the time between two zero-crossings, with the result that the grid measurement acquires these as a sudden frequency jump.
Wind turbines react, owing to the challenging requirements of the grid operator, to such events with sudden and considerable changes in power, which also include disconnection of the power feed-in in extreme cases. Said changes in power lead to changes in frequency and must be regulated by the grid operator. Such events are therefore undesirable.